Body fluids are primarily withdrawn for a subsequent analysis in order to diagnose diseases or to monitor the metabolic state of a patient. Such a withdrawal is carried out especially by diabetics in order to determine the blood sugar concentration. The aim of such a blood-sugar check that is usually carried out several times daily is to avoid hypoglycaemic states as well as hyperglycaemic states. In the case of a hypoglycaemia the patient can fall into a coma and even die since the brain is no longer adequately supplied with glucose. In contrast hyperglycaemic states can lead to long-term side-effects such as blindness, gangrenes and such like.
Consequently a frequent monitoring of the blood sugar level is an undisputed necessity. It is therefore obvious that there is an urgent need for sampling systems which are easy to operate by the user and are above all largely free of pain.
Already blood sampling systems have been known for some time in the prior art which allow the patient or hospital staff to carry out a withdrawal in a simple manner. A device suitable for this is for example the commercially available Softclix whose manner of operation is described in U.S. Pat. No. 5,318,584. This device provides an adjustment means for the depth to which a lancet is inserted into the tissue. Hence the patient can select the minimum puncture depth which enables a just sufficient quantity of blood to be obtained for a subsequent analysis and thus keep the incision pain very low. After the patient has produced a skin opening by piercing, he has to massage or press his finger in order to draw sufficient blood from the puncture wound especially with small puncture depths. This operation which is frequently referred to as “milking” by diabetics can hitherto only be avoided when the puncture is very deep and correspondingly unpleasant for the patient and can lead to major scarring on the sensitive finger tips. Devices known in the prior art attempt to stimulate the outflow of blood by applying a vacuum but this has proven to be not efficient.
Devices are also known in the prior art in which a so-called stimulator with a ring depresses the skin surface surrounding an incision site. Such a device for obtaining interstitial liquid is described for example in U.S. Pat. No. 5,582,184. The ring used to depress the skin surface is made of a rigid material. Only small amounts of fluid can be obtained with the device that are not adequate for commercial analytical systems.
Another device is known from U.S. Pat. No. 5,857,983 in which a syringe is inserted into the skin surface and the skin surface surrounding the site of incision is repeatedly depressed using a so-called stimulator in order to press body fluid into the syringe. Like the above-mentioned document a rigid ring is used in this device to depress the skin surface. The amounts of body fluid that can be obtained with this device are small and thus inadequate for conventional analytical systems.
Blood sampling devices are also described in the U.S. Pat. No. 5,951,493 which operate with a stimulator like the above-mentioned US patent. In addition a device is described in FIGS. 15 to 17 in which the area of the device that is used to press against a body surface is provided with levers (104) which laterally press together a part of the body while the device is pressed against the body surface. The devices described in this patent are in particular intended for withdrawing body fluids from other sites than the finger pad. In addition the document shows that the transport of body fluid onto the skin surface is achieved by repeated pressing of the device.
A device is known from the document U.S. Pat. No. 3,626,929 in which a finger is clamped before blood withdrawal between a lever and a finger support. The finger support is moved by a motor in order to result in a massaging proximal to the incision site. For the withdrawal the user's finger is pressed against a flexible cap in which needles and a fluid channel are located. A disadvantage of this device is that the needles for the withdrawal remain in the body and that in this state the finger support is moved. This results in the movement of the needles in the finger which usually leads to considerable pain. In addition it is extremely unlikely that blood will emerge while there is a needle in the finger so that the channel is closed by the needle. A collecting container is shown in FIGS. 11 and 12 which has a flexible pressure-application region. However, due to the shape of the pressure-application region which widens conically towards the finger there is no conversion of a primary pressure-application movement into a lateral movement which squeezes the sampling region together.